Cabin-Air Recirculation
Cabin-air recirculation is an HVAC mode that reduces or closes the outside-air intake and sends cabin air back through the climate system.
Why vehicles use it
Recirculating air that is already nearer the selected cabin temperature can reduce short-term heating or cooling demand. With the windows closed and a suitable cabin filter, it can also reduce the entry of outside smoke, dust, exhaust, or unpleasant odors. It does not make the cabin sealed or provide universal protection from pollution; the result depends on the vehicle, filter, airflow, and contaminant.
Air quality and visibility limits
Occupants add carbon dioxide and moisture to cabin air. Extended recirculation can therefore raise cabin CO2 and encourage condensation or fogging, particularly in cold or humid conditions. Outside air and the vehicle's demist or defrost mode may be needed to restore visibility.
Automatic recirculation is not one universal behavior. A vehicle may respond to pollutant, humidity, temperature, or defrost inputs, and may time out manual recirculation or prevent it in some conditions. Volvo documents one such implementation; other vehicles can use different sensors and control rules. Volvo XC60 Owner's Manual — Activating Air Recirculation
For the wider HVAC, filtration, demisting, and energy context, see Climate systems in electric vehicles.